No worries, this is an easy fix. Several members on the forum sell belt tensioner kits, Rodney Dickman has a nice one, look under "vendors" at the top of page or do a search for tensioner kits.
I wanted to keep all stock on my Fiero so I purchased a "cogged" belt, those are cogged against the main groves of the belt for extra gripping power. You can go with a "Gatorback" or a "Dayco" belt, I'm at work, just snuck outside, belt number Dayco poly cog 5050413, man alive, raining to beat the band!!!
Be sure to thoroughly clean the pulleys, nylon scrub brush, brake cleaner, get them 100% perfectly clean.
Two bolts, loosen top and lower, have a freind with a breaker bar, pole or a crow bar apply tension while you tighten adjustment bolt on bottom, then tighten top.
I swear by those cogged belts, best wishes for a speedy repair.